need input and help with where to find parts

i have a 1975 dart that im trying to sell but if i dont sell it within the next month im going to end up just keeping it. this is where i need your guys and gals help. my cousine just gave me a completely rebuilt 440 that has only been cranked on the dyno and never put in a car. i know thats awesome and all but heres my problem. i know absolutely nothing about the 440. i dont know what all modifying ill have to end up doing to the car seeing as it only has the original 225 /6 in it. i really want the power from that monsterous v-8 but i dont know if i should yank the /6 out because its the original motor and it only has just over 89000 original miles on it. its never been rebuilt or even cracked open. it still has the paint on the valve cover bolts when it was painted in the factory back in 75. so should i go ahead and rip the /6 out and put in the 440 or should i leave it the way it came? i wanna hear what everyone has to say so feel free to say whatever you want to. thanks y'all.